Objective changers of this type are known from the prior art. In addition to the known objective turrets, in which several objectives are mounted on a carrier in circular arrangement and the desired objective can be swiveled into the operating position by rotating the carrier, objective changers are known in which objectives can be individually brought from a stand-by position into an operating position which is common to all objectives.
The latter type of objective changers has proved to be advantageous in particular for applications in the field of electrophysiology since hereby a large free space around the objective and the object can be created. Typically, for applications in electrophysiology a sample stage having a sample placed thereon is no longer moved after positioning of the sample. On the one hand, this is because of the often existing touch and vibration sensitivity of the samples to be examined and, on the other hand, because of the fact that the examined biological samples are often manipulated during their observation. Such manipulations require a large free space around the object. Often, the preparation is accessed by several manipulators at the same time. Via the manipulators, for example current, voltage as well as dyes, liquids etc. are applied to the sample or substances are injected into the sample. Often, the manipulators remain in their position relative to the sample throughout the entire examination. In addition to the demand for a large free space, it has to be taken into account that there is a wish to be able to use several (i.e. at least two) objectives for object examination in order to be able, for example, to change from a general image having a low magnification to a detailed image having a high magnification.
When changing an objective, it has to be taken into account that the objectives used in electrophysiology mostly have a very little working distance to the examined preparation or even dip into the liquid often surrounding the preparation. In most cases, the preparations are placed in dish-shaped containers, the so-called Petri dishes. When changing an objective it has to be secured that the objective is raised over the edge of the container and the new objective is only lowered when it has reached the inner area of the container. In doing so, any movement of the sample stage for facilitating the objective change is to be avoided.
Against this background, DE 10 2007 042 260 A1 of the applicant suggests an objective changer having a changing device for at least two objectives in which each of the objectives can be pendulously swung into its operating position near the focal position via the changing device. From the operating position, the objectives can be swung into a stand-by position. Advantageously, the pendulous swinging motion takes place in one plane. Swinging-in of the one objective can cause the swinging-out of the other objective. In addition, the objectives can be lowered during swinging-in and raised during swinging-out. As the entire swinging area of the objectives has to be kept free of manipulators, this objective changer proved to be disadvantageous for some applications.
The swinging-out of an objective from an observation position into a stand-by position for avoiding obstructions and intersections in the case of examinations in the field of electrophysiology also represents the basic principle of the teaching of JP 09258088A.
For the examination of samples in a sample chamber filled with immersion medium, DE 10 2007 018 862 A1 suggests an objective changing device for a microscope having two fixed objectives which are arranged movably with respect to the sample chamber. By a corresponding displacement, one of the two objectives can be brought into the operating position, while the respective other one is in the stand-by position.
EP 1 168 027 B1 suggests an objective changer by means of which the longitudinal axis of the objective can be moved substantially coaxially to the optical axis of the objective for an objective change. In one embodiment, an objective can be moved along a curved guide rail, this curve extending approximately parabolically, the plane of the parabola including the optical axis of the objective and the apex of the parabola corresponding to the desired position (operating position) of the objective. In another embodiment, the objective is raised from its desired position by means of a gripper arm in the direction of its optical axis and is brought into a storage position (stand-by position) by means of a swivel arm. In still another embodiment, a selected objective is brought from a storage position via a feed channel extending coaxially to the optical axis of the objective but perpendicular to the optical axis of the microscope into its desired position, wherein it has to be erected for this purpose from a “lying position” into an “upright position” so that the optical axis of the objective coincides with the one of the microscope.
Finally, from DE 198 22 870 C2 a device for an objective change in an up-right microscope having at least two objectives and an associated focusing device is known, which can move the objective located in the active position (i.e. in the operating position) in the direction of the optical axis, as well as having a common carriage receiving the objectives in objective holders, which carriage can be moved perpendicular to the optical axis for objective change. Here, for moving the carriage one single actuating element is provided with which in addition also the desired objective can be raised or lowered and be brought into the active position. This actuating element is a rod mounted on the carriage, which rod is used as a pull rod in order to bring one of the two objectives mounted on the carriage into the operating position and the other one into the stand-by position. When rotated, the rod actuates a lever which interacts with an objective holder in order to raise or lower the same. Given this solution it proves to be disadvantageous that the two objectives are in a fixed position relative to one another so that the free working space is highly restricted because of the second objective which is located in the stand-by position and arranged in the direction of the user.